The gentoo manuals are great, taking you step-by-step through the whole process. Following this, i first needed their live-cd for booting this old pentium 166mhz. So i burned the live-cd 2004.2 iso (the minimal one).
Watch out that you burn this one as an ‘image’, so do not create a cd with the iso file on it as this does not work: you need to have a bootable cd. I used nero with the ‘burn image’ menu option. Just select the iso file and go.
With the freshly made cd I tried booting the old pentium system. It did not boot. So, was the bios set correctly? yes: bootorder CDROM,A,C That was not the issue. Maybe the cdrom was too old and dusty.. after all, the system was 8 years old. So I installed another cdrom in the system. no luck, but I found out that a fedora or redhat boot cd DID boot! So there is something wrong with the gentoo disc, as it does not boot in older systems. I made 5 copies of the CD just to be sure, but none of them would boot the old machine.
UPDATE: I did a gentoo install using the fedora boot disk – just boot the fedora boot cd in ‘rescue’ mode and start installing gentoo the moment the bash prompt is shown. Googling for other gentoo installtion info, I found out that knoppix (linux-on-a-cd) is also a good way of starting the gentoo installation, and maybe toms bootroot (linux-on-a-floppy, http://www.toms.net/rb/) might work for the older (386 and like) pc’s, although I did not try this (yet!).
UPDATE2: There is a new experimental minimal-cd available which fixes this problem.